How contagious is a cat with feline immunodeficiency virus (FIV)?

I would hate to see your daughter put such a young, beloved companion to sleep. FIV in and of itself is not painful, and the signs can be managed as they arise if she is willing to do so. You must realize however that your daughter may be ready to put this cat to sleep, now, and not agonize with a chronically ill cat through all of the emotional ups and downs. The danger to your cats is minimal, especially if you are able to separate them. FIV is transmitted primarily by bite wounds, and is therefore not aseasily acquired as FeLV. If she decides to try and treat, I would start the cat on a high quality, high protein diet such as human baby food (no cat food), or home-cooked wet rice/chicken or turkey with added enzymes. Coenzyme Q-10 10mg/day will help with the gum disease. I would also start her on a course of supplements/immune enhancers such as Interferon (which your vet can make up), dimethylglycine, and Pau D'Arco. These are all liquids so they can be administered relatively easily without having to pill her.